Abstract
Plant production in microgravity is essential for sustaining astronauts long-term space missions. However, previous containerized plant cultivations in space has yielded inconsistent results, largely due to challenges in understanding the hydraulic properties of porous media, particularly water retention characteristics (WRCs) and hydraulic potential (H) under microgravity. This study addresses the issue of over-fertigation in the root zone, a persistent challenge in past space-based systems. We propose an on-demand passive fertigation system, regulated by a check valve-controlled H and tailored to the WRCs of the porous medium. Our system consists of 1) H regulation via a coupled check valve and porous membrane, 2) a water reservoir (collapsible for μg) and 3) containerized porous media. We determined target matric potential values for three particle size ranges of aggregated calcined clay to maintain adequate volumetric water content during 60 days of continuous romaine lettuce cultivation. This system supplies water only within a range of H, associated with the opening and closing of the check valve, requiring no automation or power. The findings could be adapted to reduced gravity (lunar or Martian) conditions. While this study establishes a foundation for on-demand fertigation, further research is needed to refine check valve characteristics for long-term cultivation.